1. Field of the Invention
This invention relates to a two-piece motor stator having outer and inner iron stator cores which are combined into one body by fit.
2. Description of the Prior Art
Various types of two-piece motor stators are known which are mounted in a stationary motor housing together with a rotatable rotor. The techniques of two-piece motor stator, i.e., dividing a stator core into outer and inner cores, is used for making the motor smaller and for lowering the manufacturing cost. Such a stator comprises an inner iron stator core having a plurality of teeth and an outer iron core having a plurality of slots for engaging the outer iron stator core with the same with the tip of each tooth fitted into a corresponding slot. At first, a wire is wound on each tooth to form a coil. Then, the inner iron core is engaged with the outer iron core by press fit. This structure makes the winding process easier, thereby lowering manufacturing cost.
FIG. 9 shows such two-piece motor stator combination in a fragmentary perspective view. An annular outer laminated iron core 1 is made of iron plates. Inside the outer iron core 1, a generally annular inner iron core 2 is provided with the central axis thereof coincident with that of the outer iron core 1. The outer and inner iron stator cores 1, 2 are combined by press fit, as shown in FIG. 9. The resultant stator core is assembled in an unshown motor housing together with an unshown rotor with the central axis of the outer and inner iron stator cores 1, 2 coincident with the rotation axis of the rotor. The inner iron core 2 has a plurality of teeth 5 extending radially outwardly from the outer surface thereof. A coil 3 is a wire wound around a tooth 5 of the inner iron core 2. A slot 4 is made in the inner surface of the outer stator iron core 1. The tooth 5 is provided for engaging with the slot 4. The slot 4 is formed to be complementary to the tip of the tooth 5 in cross-sectional shape. Therefore, the outer iron core 1 can be engaged with the inner stator iron core 2 with the tip of the tooth 5 fitted into the slot 4.
However, in such two-piece motor stator, the above-mentioned structure causes deformention at the inner peripheral portion of the inner iron core 2 and the outer peripheral portion of the outer iron core 1. The deformation of the former portion causes an increase in motor-running noise level, while the deformation of the latter portion results in difficult assembling.
The reasons for the deformation are as follows:
The outer and inner iron stator cores 1, 2 are engaged with the slot 4 fitted with the tooth 5 by transition or interference fit. Therefore, a considerably large power is required for fitting. Such a fit requiring large power causes stress in the outer and inner iron cores 1, 2, thereby generating such deformation.
Therefore, in the prior art two-piece motor stator, there is a drawback that undesirable deformation of the stator iron core deteriorates the performance of the motor.